1. Field of the Invention
The present invention relates to a biological information measuring apparatus for acquiring various types of biological information associated with the metabolism of a living organism, such as biological density, water content, blood oxygen level, glucose level, blood glucose level, and pulse, on the basis of the mechanism that the transmission of light through a living organism necessary signal with wavelength of the light; and to a method for controlling the apparatus.
2. Background Art
In recent years, there have been actively proposed, as an apparatus and method for conveniently analyzing the interior of a living organism in a noninvasive manner, apparatuses and methods for acquiring information on the interior of a living organism by emitting light from a light source provided on the surface of the living organism to the interior of the organism, and receiving reflected light which has been transmitted through the living organism while being scattered and absorbed therein, and which has reached the living organism surface. For example, Japanese Patent Application Laid-Open (kokai) No. 2000-172407 discloses a biological optical measuring apparatus including, as main components, a semiconductor laser, a modulator, an optical fiber, a photodetector, and a multi-channel lock-in amplifier. Particularly, this biological optical measuring apparatus can acquire information on, for example, cerebral activity at the cerebral cortical layer through measurement of blood oxygen saturation on the basis of a change in absorption of near-infrared light by hemoglobin.
In the apparatus disclosed in Japanese Patent Application Laid-Open (kokai) No. 2000-172407, the multi-channel lock-in amplifier selectively detects beams of light which reach the photodetector. However, this apparatus may fail to eliminate adverse effects on measurement caused by, for example, mutual interference (crosstalk) between light beams emitted from the semiconductor laser, or outside light (e.g., light from an inverter-type fluorescent lamp), leading to limited measurement accuracy.
Japanese Patent Application Laid-Open (kokai) No. 2003-207443 discloses an optical measuring apparatus including at least one of a plurality of amplification means and a plurality of attenuation means, the amplification means respectively amplifying signals measured at light-receiving sections, and the attenuation means respectively attenuating the intensities of light beams entering the light-receiving sections. This optical measuring apparatus can maintain the intensity of necessary signals at an optimal level by varying the amplification factor of the amplification means or the attenuation factor of the attenuation means in accordance with the light emitting/receiving conditions, which change during the course of measurement. Meanwhile, Japanese Patent Application Laid-Open (kokai) No. 2004-248849 discloses a multi-channel optical measuring apparatus in which the arrangement of light-emitting points and light-receiving points is optimized in a probe, whereby a light-receiving point receives light emitted from a specific light-emitting point. In this multi-channel optical measuring apparatus, light-emitting points and light-receiving points are arranged so as to form a pattern of equilateral triangles, whereby the distance between a light-emitting point and a light-receiving point is optimized, and at the light-receiving point, light emitted from the specific light-emitting point is received.
However, in the optical measuring apparatus disclosed in Japanese Patent Application Laid-Open (kokai) No. 2003-207443 or the multi-channel optical measuring apparatus disclosed in Japanese Patent Application Laid-Open (kokai) No. 2004-248849, a necessary light beam is selectively received merely by varying the intensity of light emitted from a light-emitting point as measured at the corresponding light-receiving point. Therefore, a light beam to be received (necessary light beam) is not actively identified, and thus adverse effects of light crosstalk or outside light on measurement may fail to be avoided.
In order to solve the above-described problems, the present applicant has proposed a biological information measuring apparatus and a measurement method employing the apparatus, which are disclosed in Japanese Patent Application Laid-Open (kokai) No. 2002-248104. Specifically, this biological information measuring apparatus includes a light emission section which emits light which has undergone spread spectrum modulation by use of a pseudo-noise sequence; and a light detection section which receives the spread-spectrum-modulated light, and outputs a detection signal obtained through despreading of the above-modulated signal. The biological information measuring apparatus and measurement method can eliminate light beams which do not have the same pseudo-noise sequence, and thus can actively avoid adverse effects of light crosstalk or outside light on measurement.
In the case where multi-channel measurement is to be performed by means of the biological information measuring apparatus described in Japanese Patent Application Laid-Open (kokai) No. 2002-248104, in which the light detection section identifies light beams having two wavelengths emitted from the light emission section, a number of combination units, each including the light emission section and the light detection section, must be arranged. Therefore, the apparatus may become large in size, and multi-channel measurement may become physically difficult. Recently, particularly, demand has arisen for an apparatus which enables measurement of biological information with improved accuracy, and real-time observation of detailed measurement results.